[e2e] purpose of pseudo header in TCP checksum

Joe Touch touch at ISI.EDU
Tue Feb 15 09:38:33 PST 2005

Michael Welzl wrote:
>>In IPv4, the IP header checksum does cover the SA/DA - it covers
>>everything in the IP header, including the hop count. In IPv6, there is
>>no header checksum, of course.
> ...which was a bad decision IMO, because it breaks the
> "IP over everything" model and will now lead to problems
> with mechanisms such as UDP Lite, where link layers are
> now required check the headers (but ONLY the headers)
> of things above. Yuck.

IPv6 _requires_ UDP checksums. UDP Lite already addresses this, and when 
used ALWAYS INCLUDES the pseudoheader. See RFC 3828.

IP still works over everything; things that work over IP need to know 
something about it, as always.

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